1. Field of the Invention
The present invention relates to a photoelectric converting apparatus having a plurality of photosensors which are divided into an opening portion and a light shielding portion.
2. Related Background Art
FIG. 1 is a schematic constitutional diagram of a conventional photoelectric converting apparatus having the dark output compensating function.
In the diagram, a sensor section 1 comprises cells S.sub.1 to S.sub.n in the opening portion to perform photoelectric conversion and a cell S.sub.d in the light shielding portion to obtain a dark reference output.
Signals of the cells are sequentially output by a scan section 2 and input to a dark output compensation section 3. The dark output compensation section 3 subtracts a dark reference signal amount of the cell S.sub.d from the signals of the cells S.sub.1 to S.sub.n and outputs the result.
Since the output of the sensor cell S.sub.d in the light shielding portion corresponds to a dark current of the sensor cell, by subtracting the dark reference signal amount of the cell S.sub.d from the signals of the cells S.sub.1 to S.sub.n, the noise components of the dark current are eliminated. Thus, a photoelectric conversion signal which accurately corresponds to the incident light can be derived.
A clamping circuit can be used as the dark output compensation section 3, or it is also possible to use a sample and hold circuit to hold the dark reference signal of the cell S.sub.d and a differential circuit to obtain the differences between the dark reference signal and the signals of the cells S.sub.1 to S.sub.n.
FIG. 2 is a schematic cross sectional view of the sensor section 1 in the foregoing conventional apparatus.
In the diagram, the sensor cells S.sub.d and S.sub.1 to S.sub.n are formed in a line in an n.sup.- layer 701 through device separating regions 702.
Each cell has a p region 703 to accumulate the carriers generated by the light excitation. A light shielding film 704 is formed on the cell S.sub.d, thereby constituting a light shielding portion.
However, the foregoing conventional photoelectric converting apparatus has a problem such that when strong light enters the opening portion, the carriers leak from the opening portion to the light shielding portion and exert an adverse influence on the dark reference output.
Namely, as shown in FIG. 2, when the strong light enters and the excess carriers (in this case, holes) are accumulated in the p region 703 of the cell S.sub.1 in the opening portion, these excess carriers 705 flow out to the side of the n.sup.- layer 701 and flow into the p region 703 of the cell S.sub.d in the adjacent light shielding portion. Thus, the dark reference output of the cell S.sub.d changes and the foregoing accurate dark output compensation cannot be performed.
The foregoing conventional photoelectric converting apparatus also has the following problems.
First, there is a case where a part of the holes generated in the substrate by the incident light move in the substrate and flow into the adjacent pixel.
Second, when the strong light enters, a large quantity of holes are accumulated in the p base region, so that the base potential increases. When the base potential rises to a value higher than the collector potential, the depletion layer between the base and the collector is extinguished and the holes accumulated in the base flow out to the adjacent cell.
As explained above, when the holes moved from the other pixel flow into the p base region of the adjacent cell, the readout signal of this pixel does not correspond to the incident light, resulting in a smear when an image is reproduced, so that the picture quality remarkably deteriorates.